Steam and gas turbines operate at high pressure and temperature conditions, and their constituent parts are subjected to significant mechanical and thermal stresses and deformations. In spite of such conditions, proper alignment and concentricity of turbine components must be maintained to ensure minimal clearances between stationary and rotating parts.
Turbine cases often utilize a multi-shell “matryoshka style” design consisting of several separate casings nested inside each other, thereby reducing peak stresses by dividing the entire pressure/temperature drop across several casings. An inner casing is aligned with an outer casing in the so-called “thermal cross” manner, i.e. with interconnections at two mutually perpendicular (e.g. horizontal and vertical) planes. The interconnection at the horizontal plane is made as the centerline suspension which carries both dead weight and reaction loads from rotor rotation and maintains alignment in the vertical direction, with vertical keys being located at the vertical plane for maintaining alignment in the horizontal direction.
FIG. 1 illustrates one such prior art horizontal joint suspension arrangement 10 wherein a portion of the inner casing flange 12 extends into a slot 14 formed in the outer casing. This arrangement functions well, but it requires an increase in the casing size and it significantly complicates the machining of the casing.
FIG. 2 illustrates another prior art horizontal suspension arrangement 16 that has been used for retaining the stationary components such as the diaphragms, labyrinth boxes, etc. inside of the outer casing. These stationary components are not bolted together at the joint. This suspension arrangement permits the upper half 20 of the outer casing to be used together with the upper halves of the diaphragms, labyrinth boxes, etc. during handling and assembly of the casing. The entire inside stationary component (upper and lower halves) is suspended in the lower half 21 of the outer casing by means of a support member 23 that is installed loosely into a shallow groove 27 which is formed in the lower half of the stationary part 30, and is welded 26 to this half. The protruding portion of the support member is extended into the slot 35 formed into the lower half 21 of the outer casing and is rested on the shim 31 which allows for proper alignment between the outer casing and the diaphragm, labyrinth box, etc. The upper half of the diaphragm, labyrinth box, etc. has a similar support member 24 installed into the shallow groove 28 and welded to this half with a shim 29 for alignment. The protruding portion of this support member is also extended into the slot 33 formed in the upper half 20 of the outer casing. This protruding portion is facing a separate key 18 that is attached to the upper half 20 of the outer casing by a bolt 22. The key 18 carries the weight of the upper half of the diaphragm, labyrinth box, etc. during handling and assembly operations as the upper half of the outer casing is being carried on and installed onto the lower half of the outer casing. During such handling operations, gap 15 will be closed as key 18 lifts against support member 24. After assembly and once the outer casing halves are bolted together, these components do not carry loads during turbine operation, since the upper half of the diaphragm, labyrinth box, etc. is resting directly on its lower half. This arrangement would not be useful as a casing support because it would be too flexible due to the loading of the bolted joint.
FIG. 3 illustrates another prior art horizontal support arrangement 32 incorporating a separate support member 34, but with the support member being bolted into the inner casing 36. While this arrangement is more robust than the arrangement of FIG. 2, it is nonetheless susceptible to significant vertical deflection when loaded under the weight of an assembled turbine and the reaction load from rotor rotation due to the moment loading imposed on the bolted support arrangement.